This invention relates to a paint system including a flexible conduit or hose arrangement to supply a liquid coating composition from a paint supply system to a spray gun. More particularly, this invention relates to an improved spray gun for the paint system.
As those familiar with the prior art will appreciate, in previous paint supply systems, a base coat of paint is applied at a first station and then the article, such as an automobile body, is conveyed to a new station where a clear coat paint is applied, the clear coat paint adding the feeling of depth to the paint. The ability to apply a clear coat and a base coat at the same time would provide a dramatic reduction in the cost of painting the car in the sense that half of the spray booths could be eliminated or deactivated and therefore half of the equipment and half of the manpower could be eliminated from the painting operation.
Additionally, the modern factory is typically spread out and paint booths are not localized in one area or arranged so as to be parallel to one another. As a result, the use of a series connection between paint booths requires extensive tubing, particularly when the paint must be supplied to opposite sides of each booth. Accordingly, it would be desirable to minimize the number of lines needed to supply paint in a paint system and the cost associated with these lines.
A continuing problem associated with the spray application of liquid paints is the presence of foreign particulate matter in the liquid paint supply which causes imperfections on the surfaces of the article being spray painted, frequently necessitating a refinishing or repainting thereof. Such foreign particulate matter, sometimes referred to as "seeds," or "strings," or "snotters" are formed in many instances as a result of an agglomeration of the paint constituents during standing or recirculation of the liquid paint necessitating removal prior to discharge through the spray nozzle. The foregoing problem is particularly pronounced in recirculating type liquid paint systems, although they are present in direct line systems as well.
Recirculating paint supply systems conventionally comprise a mixing tank equipped with suitable agitation for maintaining the liquid coating composition uniformly mixed and a pump for transferring the liquid coating composition under a desired pressure to a manually manipulable supply conduit connected to the spray nozzle. A suitable return hose is provided for returning the excess quantity of paint back to the mixing tank for recirculation and to keep the paint in suspension. Typical of such a system is the recirculating paint supply system shown in U.S. Pat. No. 5,060,861, the specification of which is incorporated herein by reference. In this paint supply system, the supply and return hoses are interconnected by suitable fluid fittings so as to form a single conduit having coaxial passages for supplying and returning the liquid composition.
This and like paint systems typically will utilize many different fittings, connectors and coupling arrangements to complete the necessary fluid interconnections. Such fittings are often generally made of metal which can result in the conduit being relatively heavy. However, the paint supply hoses or unitized fluid conduit, and the associated fluid fittings, should be as light as possible to reduce operator fatigue and enable the operator to manipulate the position of the spray gun.
Moreover, conventional spray guns are also generally made of metal which results in the spray gun, including the fittings to be relatively heavy. This weight may cause operator fatigue or ailments based upon the continuous and repetitive use of the heavy spray gun, which typically weighs about 22 ounces. Still further, as the work day draws on, this fatigue increases which may cause an appreciable decrease in finish quality of the object being coated. This decreased quality generally occurs because the operator may angle the spray delivered from the spray gun as opposed to maintaining the spray substantially perpendicular to the object which is desired.
Seals and filters are also included in the paint supply line to seal the interconnections as well as to remove particulate matter from the paint being provided to the spray gun. In spite of the seals and filters, foreign matter can still be present. For example, the quick connectors used for the spray gun tend to create spit at the quick disconnect upon disconnecting which is generally not noticeable but, when dry, will cause leakage and contamination to occur. Further, to prevent leakage, it is known to cover the threaded sections of fluid fittings with pipe dope and then assemble the fittings. While this arrangement works well in many fluid sealing applications, it has several disadvantages. First, a pipe fitter must be called to assemble or disassemble the unit, which can be an inconvenience. Further, exposed threads create voids in the joint between the components which causes paint to accumulate and generates paint particles (dirt, etc.) that will be sent downstream and end up on the car, resulting in the need to rebuff and/or repaint the car.
Various flow control devices or paint restrictors are also used with paint supply systems. In many cases such prior art constructions have been handicapped by their tendency to become plugged over periods of use, necessitating frequent replacement and/or downtime to permit cleaning to restore them to proper operating conditions. The build up of deposits in such flow regulators cause a progressive decrease in the pressure of the liquid coating composition supplied to the spray nozzle, thereby resulting in variations in the quality and thickness of the coating, thus detracting from their use.
Moreover, a flow control device must include an element that moves relative to its valve body in order to change the flow rate. For example, a conventional ball valve has a rotatable ball member through which fluid can flow and seal portions positioned at the opposing upstream and downstream faces of the ball to inhibit flow therearound. Extended use of the valve member in one flow position can result in paint coagulating in voids formed around the seal portions. When the ball member is rotated, paint portions can break loose, thus detracting its use. Paint flakes, particles and dirt can result from the mating of fluid connector members, notwithstanding a seal being positioned to prevent flow around mated portions.
Accordingly, it would be desirable to limit or replace the use of threaded fittings with compression fittings, or those that use only pressure, thereby eliminating voids which tend to cause the paint to accumulate.
Moreover, it would also be desirable to reduce the weight of the conventional spray gun and fittings, thereby reducing operator fatigue and increasing finish quality.